I'll take a stab at the "theoretical underpinnings" part of your question vis-a-vis higher intake than exhaust lift. I was asking questions comparing two cams with very similar intake lift, duration and timing but one having longer exhaust duration and more overlap while the other was "symmetrical". Besides the difference in overlap the other factor noted was that the shorter exhaust duration retained more heat in the combustion chamber, thereby producing more low end power. I suspect the same applies in the case of lower exhaust lift, and possibly to a higher degree. As long as the exhaust valve is held open long enough to evacuate all the spent gases and not contaminate the intake charge, I guess keeping more combustion heat in the chamber results in more torque. I'm guessing that this has to be pretty well matched to the heads' flow characteristics, which probably goes back to the realm of proprietary info and why many of these guys sell packages. Their cams are designed to work well with their heads. I'm guessing timing has to be carefully tuned as well in this case; it seems to me that an engine like this would tolerate less advance than one with longer exhaust duration... Somebody help me out here if I'm off target... I'm not professing to be an expert here, this is what I've gathered from talking with others who I consider to be experts.

 

You are pretty much on the money. I am more familiar with HQ cams than other brands. For example the HQ500 and 575s are designed to produce torque much lower in the power band than equivaent designs and both do require less timing advance for optimum performance. I was amazed at how little advance I ran in the cruise range of my 120 with the HQ 575s and yes, they will work well with other head designs but really shine when used with HQ heads. I am sure that Hillside has a very specific head design in place when using say a Wood 6 vs a Wood 8 or a build they are doing with Andrews cams. Thier "package" may not be all one manufacturer but they know from experience what does and does not work well together and what the head requirements are.

Bottom line is that there are many "science projects" that are put together by individuals without the knowledge or on the say so of a HD tech that doesn't have a lot of build experience under their belt. Those project may run ok, but when measured up against a true package build by a reputable builder, those science projects fall short.

 

Maybe, maybe not; I think you know that flow (CFM) is not a function of lift. Just because there is addtional lift at all points off the base circle does not necessarily mean more flow. It will take all the components, i.e., head porting, intake flow capacity, exhaust scavenging/reversion and mainly the intake close and exhaust open timing.

Only one way to find out, before and after dyno rockers being the only change.

I don't know if there is an "optimum" ratio of intake to exhaust; however, if there is, it will probably vary from one build to the next. I think every porter strives for that optimum but they can achieve something on a flow bench that may or may not be replicated in the motor due to intake, exhaust and valve timing; in most cases, I would guess not.

There are two camp profiles that fall into the category I think you are referring to.

Asymetrical - Cams with different lifts for intake and exhaust
Dual Pattern - Cams with different duration for intake and exhaust

The 1.7 rockers will replicate an asymetrical profile but I am not sure how that will work with your particular combination of parts. Like I said, only one way to find out.

I don't see any benefit from a 50mm TB until you improve the head flow. If you move forward to test your theory, do it one step at a time so the results will mean somthing. Keep us posted.

 

Saw on another thread that the stock pre-'06 throttle body flows 184 CFM (on a flow bench) ... so if the max flow of my heads is 230 CFM, seems the T/B is a 'bottle neck' ....

On the flow bench, the 50mm T/B flows 232 CFM ... therefore, my conclusion is that the 50mm would be a good 'flow match' for my setup ....

Appreciate responses fellas ... I'm dropping the rockers in (intake side) tomorrow morning ....

I'll keep you posted ... when the weather in VA improves ....

R/
'Chop

 

What size are the injectors in the 50mm TB? Any difference in performance cannot be attributed to inreased flow if the injectors are larger, even if pulse width remains the same; just saying.............

 

Okay - initial trip report ... just got the 1.725 rocker arms installed (intake side only) this afternoon and went for a little 20 mile putt ....

I did not change the map I was running in my ThunderMax with AutoTune ECM ... I figured the auto-tune feature would sense the AFR and add fuel ... I suspect this was proven to be the case, as it took a little more turning over to hit off on start-up ... then it seemed a little hesitant on the first couple of throttle twists ....

I let it warm up a few minutes ... and it didn't take long for it to settle into a good sounding rythm.

The motor seemed to produce a little more sound volume and sported a slightly lower exhaust note ... I was a little concerned for about 5-10 seconds at start up it seemed to make a little valve clatter sound that quickly went away ... I presumed it just took a few seconds for the oil to make it to the top end and quiet things down up there ... I did not check to see if there was a requirement to clearance the rocker cover for the 1.725 rocker arms ... but, apparently not since the noise went away quickly and did not recur ....

I had not riden my bike in about a week ... now, I have been quite pleased with my 'science project' build before this ... and I have never had my bike on a dyno ... so, my 'butt dyno' perception that this has been an improvement may just be an example of the 'placebo effect' ... but, I really enjoyed the ride and feel like adding the 1.725 rocker arms was a noticeable improvement ....

I think one thing that will demonstrate in my mind how much of an effect this has had will be to download the map from the ECM module to my laptop ... if there are a whole slew of points adding fuel to the map, that would indicate to me that the increase in air through the motor is significant ....

* * *

djl

I think the 50mm T/B sports the 25* injectors vice the earlier 8* injectors in my stock T/B ... however, I have seen somewhere (don't recall where off hand) an analysis of the capacity of the early vice late injectors and the late style actually have less capacity ... the thing is there are almost no circumstances under which the capacity of either injector is actually approached ....

** '05 - 8* flow 4.35 gms/sec
'06 - 8* flow 3.91 gms/sec
'06 late - 25* 4.89 gms/sec

There may be something to the thought that the better atomized fuel shows a slight improvement ... I still think that if the T/B is a restriction on performance it should be addressed ... in my mind the better fuel atomization is just 'gravy' ....

R/
'Chop

 

OK, trying to learn something here as you are ahead of me on the whole EFI thing. The information above begs the question why there is a difference in injectors if the capacities are the same and/or the capacity is never tapped?

 

For real or only theoretically?

 

See #15 and #16. I had suggested that he use the same injectors when he swaps to the 50mm TB so any measureable results could be directly attibuted to the increase in TB. I think what he says in #16 is that it doesn't matter for the reasons stated.

That begs the question, at least for me, why are there different injector size? So, I am talking "for real".